Alpha4

From this version, WorkScript is switched to LLVM instead of the intepreter.
The grammer is not changed although some rules are more restrictive, such as the static type.
For reason of compilation, WorkScript now support calling external functions. It do not output binary object files, so that it could not be linked now, but it should be done in the next version.
Alpha4 is not a complete featured version and it's just for a preview. Therefore, an amount of bugs may exist, which even not existed in the previous version. If you meet a bug, please report it as issues.
What's more, the compiler can report more bugs now as it used to abort once meeting one error, so that it's more useful now.